As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased. Among them is a lithium secondary battery having high energy density and voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as the mobile devices.
On the other hand, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to the overcharge of the battery, the overcurrent in the battery, or other physical external impacts applied to the battery. That is, the safety of the lithium secondary battery is very low. Consequently, the lithium secondary battery includes a positive temperature coefficient (PTC) element and a protection circuit module (PCM) as safety elements for effectively controlling an abnormal state of the battery, such as the overcharge of the battery, or the overcurrent in the battery. The PTC element and the PCM are connected to the battery cell.
A plurality of connection members are required to electrically connect the safety elements, including the PTC element, to the battery cell. As the connection members, nickel plates are generally used. However, it is difficult to fix the nickel plates to a battery case, which is made of aluminum, by welding. For this reason, a nickel clad member is coupled to one side of the top of the battery cell, and then the nickel plates are fixed to the nickel clad member by welding. Consequently, a plurality of members are used, and therefore, a dead space increases, with the result that the assembly process of the battery is complicated, and the capacity of the battery is reduced.
Generally, it is required for the safety elements, such as the PTC element and the PCM, to be maintained in electrical connection with electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. Consequently, a plurality of insulative members are required to maintain such isolation. Generally, an adhesive is applied between the battery cell and the insulative members such that the insulative members are fixed to the battery cell by the adhesive. However, this coupling method complicates the assembly process of a battery pack and reduces the strength of the battery. When physical impacts are applied to the battery cell, the reduction of the coupling strength induces the occurrence of a short circuit in the battery cell, with the result that the battery may catch fire and explode, and therefore, the safety of the battery is lowered.
For this reason, much research has been carried out to reduce the number of the insulative mounting members, which are coupled to the battery cell, such that the assembly process of a battery pack is simplified, and, at the same time, to improve the mechanical strength of the battery cell. For example, Korean Patent Application Publication No. 2002-077175 discloses a structure in which lock protrusions are formed at a battery case or a cover, which is mounted to the top of the battery case, and lock receiving parts are formed at the cover or the battery case, such that the cover is coupled to the battery case by the engagement between the lock protrusions and the corresponding lock receiving parts. Korean Patent Registration No. 0561298 discloses a structure in which concavo-convex parts are formed at the coupling interfaces between a bare cell and a battery component section located at the top of the bare cell such that the battery component section is coupled to the bare cell by the engagement between the concavo-convex parts of the bare cell and the corresponding concavo-convex parts of the battery component section. Also, Japanese Patent Application Publication No. 2006-140149 discloses a structure in which a protecting cover is coupled to a cell by the engagement between a conductive press member, mounted to the terminal part of the cell and a conductive insertion member, which is inserted into the conductive press member.
However, the above-described technologies do not suggest a battery pack structure that is capable of providing a desired effect.
Consequently, there is a high necessity for a battery pack structure that is capable of reducing the number of members mounted to the top of the battery cell to simplify the assembly process, providing a desired weldability, and exhibiting an excellent structural stability against an external force.